Transistor headlamp beam control



Nov. 28, 1967 J. H. GUYTON ET AL 3,355,624

TRANSISTOR HEADLAMP BEAM CONTROL Filed June 1, 1965 AMPLIFIER A T T w.

j an fi zz i IN VEN'IORS 20 I J QFQ, 5 Jimm A. Gayfozz, 6

AT 7' OM51 United States Patent 3,355,624 TRANSISTOR HEADLAMP BEAM CONTROL James H. Guyton and Richard L. Jenkins, Kokomo, Ind., assignors to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed June 4, 1965, Ser. No. 461,272 6 Uaims. (Cl. 315-83) ABSTRAQT OF THE DISCLOSURE Transistor control circuit for automotive headlamps having separate high and low beam filaments. Switching transistors are connected in the filament supply circuits and are interconnected with biasing circuits to be alternatively conductive according to the condition of a control relay. Three embodiments are disclosed in detail.

This invention relates to transistorized switching means and more particularly to transistorized switching means for use in controlling the lighting systems for automotive vehicles.

Automatic light sensitive headlight dimming systems are currently offered which control headlamps of automotive vehicles causing a switching from high beam filament energization to low beam energization upon the approach of a vehicle from the opposite direction and a return to high beam energization when the approaching car has passed. Such systems conventionally use a light controlled sensitive relay which in turn controls a heavy power relay that actually switches the headlamp circuits. This power relay is an expensive, heavy duty, rugged component. It adds considerable cost to the system. It must be sufiiciently biased in either direction to hold against its fixed contacts firmly so that the lights will not flicker.

It is an object in making the present invention to provide a transistorized switching circuit which may be substituted for the power relay in automatic light controlled circuits for dimming headlamps.

It is a further object in making this invention to provide a solid state switching system for controlling light circuits in which there are no moving parts in the final circuit to the headlamps.

With these and other objects in view which will become apparent as the specification proceeds, our invention will be best understood by reference to the following specification and claims and the illustrations in the accompanying drawings, in which:

PEG. 1 is a transistorized control circuit for multiple filament lamps embodying our invention;

FIG. 2 is a similar circuit showing a modified form of our invention; and

FIG. 3 is a circuit similar to FIG. 2 but adapted to carry the heavier currents such as those required for a four headlamp system.

As previously mentioned, it is assumed that a light sensitive control system is present and that as variations in its output occur due to the change in level of ambient light a sensitive control relay included therein will open and close its contacts. In FIG. 1 such a sensitive control relay is shown at 2 which includes an operating coil 4 and a movable armature 6 which is adapted to engage a fixed contact 8. The movement of the armature 6 to a position in contact with stationary contact 8 and to a position separated therefrom is designed to cause a change in the energization from one set of filaments to another, such for example as upper beam to lower beam. This control system utilizes two transistors 10 and 12. The transistor 10 has its emitter 14 connected directly to power line 16 which in turn is connected to the source of power 3,355,624 Patented Nov. 28, 1957 indicated as +A. Collector 18 of transistor 16 is connected directly to the upper beam filaments 2t) and 22. Thus when transistor 10 conducts the upper beam filaments will be energized. When it is non-conductive they will be de-energized. In like manner transistor 12 has its emitter 24 connected to the power line 16 and its collector 26 connected to the lower beam filaments 28 and 30 and controls their energization. Base electrode 32 of transistor 10 is connected through resistor 34 to ground and also to stationary contact 8 of the control relay 2. Base 36 of transistor 12 is connected to a midpoint between resistors 38 and 40 which form a voltage divider, the remaining terminal of resistor 38 being connected to the power line 16 and that of resistance 40 to collector 18.

With the armature 6 out of contact with stationary contact 8 the system is so balanced due to the values of the resistors that transistor 10 will conduct and transistor 12 will be held non-conductive. While the specific values of resistances 34, 4t] and 38 may be varied considerably, the following set of values have been found to be satisfactory.

Resistor: Ohms 34- 10 40 20 38 4.7

With the relay switch 2 open and the +A line connected to a power source the base 362 of transistor 10 is connected to ground through the low resistor 34 and is, therefore, slightly negative with regard to the +A line and transistor 10 conducts, causing energization of the upper beams 20 and 22. At the same time the voltage divider formed by resistances 38 and 4-0 hold base 36 of transistor 12 at approximately +A line voltage so tran' sistor 12 is biased off and the lower beams are de-ener' gized. This would be the normal condition when the car is being driven down the road and no car was approaching. Upon the approach of a vehicle from the opposite direction operation of the light sensitive circuit will cause switch 6-8 to close. The base 32-emitter 14 of transistor 10 is now shorted and transistor 10 ceases to conduct. The upper beam filaments 20 and 22 are, therefore, deenergized. However, base 36 is connected to and grounded through the upper beam filaments. This causes the bias on transistor 12 to change and transistor 12 now conducts to cause energization of the lower beam filaments. Thus as the switch 6-8 opens and closes transistors Ill and 12 will be alternately made conductive and non-conductive to switch the headlamps between high and low beam energization. This relatively simple circuitry having no movable parts except for the sensitive relay contact can, therefore, replace the expensive, bulky power relay.

It is obvious that the sensitive relay can be inserted into various portions of the basic circuit to control the same. FIG. 2 shows a modification where the relay contacts 6-8 have been moved to a position in the baseground circuit instead of the emitter-base circuit. In this case similar reference characters will be used for identical parts where they appear. Stationary contact 8 of the sensitive relay is connected directly to the base 32 of transistor 10 and a different resistor 42 of higher value than the others is now connected between base 32 and emitter 14. The same two resistances 38 and 40 forming a voltage divider are still connected between the power line and collector i8 and their intermediate point is connected directly to base 36 of transistor 12. Movable armature 6 of the relay 2 is connected to ground through resistor 34and a new jumper resistor 44 of very low resistance is connected between collector 1:8 and the junction of the movable armature 6 and resistor 34.

With the relay switch 6-8 open in this version of FIG.

2 the lower beam control transistor 12 is conducting since the base return to ground from base 36 is through resistance 40 and upper beam filaments 20, 22 are sufficient to bias transistor 12 properly for such conduction. At this time transistor is nonconducting due to the fact that its base 32 and emitter 14 are practically at the same potential and the grounding line is open at 68 and the upper beam filaments are de-energized. In this instance this would be the condition when a car was approaching from the opposite direction and the light sensitive circuit was so designed as to open the light sensitive switch rather than close the same under these conditions. Upon a change in ambient light condition such as to cause the sensitive relay to cause contact 68 to close, the grounding circuit for the base 32 of transistor 10 is completed applying a forward bias thereto and transistor 10 begins to conduct. As the collector voltage rises due to such conduction the resistor 44 becomes inoperative since both ends are practically at the same potential and the conventional resistor 34 keeps the base current and also the collector current at saturation energizing the higher beam filaments. This change in potential at the collector changes the potential on base 36 of transistor 12 causing that transistor to cut off, de-energizing the lower beam. The use of the low resistance 44 causes a faster rise and faster switching. This resistor is effective for only a short time.

In many current headlighting systems when the socalled upper beam filaments are energized there are actually four sets of filaments energized for high beam use instead of the previous two. This creates a relatively heavy load. FIG. 3 shows a further embodiment of my invention in which two transistors are connected in parallel to carry the additional upper beam load. Therefore, instead of merely having a single transistor, such as 10 in FIGS. 1 and 2, to control the upper beam load there are now provided two transistors 10 and 10' in. parallel for controlling said load. Other than that FIG. 3 shows basically the same circuit as that of FIG. 1 and operates in the same manner, with the exception of a new resistance 46 which is connected directly between the collector 26 of transistor 12 and the bases 32 and 32' of the transistors 10 and 1%. This causes a somewhat similar result to the use of the low resistance in the circuit shown in FIG. 2. This resistance 4-6, however, is a higher resistance. For example, it might be some ohms and it will aid the maximum resistance for the relay circuit when the contacts are shorted. Any bias will result in unwanted collector current when the upper beams are ofi. Other than that the operation is the same as FIG. 1.

Through the use of these circuits the expensive and heavy mechanical power relay equipment can be replaced by relatively simple solid state circuitry to perform the desired operation.

What is claimed is:

1. In circuit control means, first and second sets of light filaments producing different amounts of illumination, which sets it is desired to energize alternately, a source of electrical power, first and second transistors each having a pair of output electrodes and a control electrode, the output electrodes of the first and second transistors being connected between the source of electrical power and the first and second sets, respectively, to control the flow of current thereto, biasing means interconnecting the source of electrical power and the control electrodes of the transistors so that the latter will be alternately conductive and the sets connected thereto alternately energized, and switching means connected to the biasing means to change the latter so that the conducting transistor will become non-conducting upon operation thereof and the non-conducting transistor conducting to alternately energize the sets.

2. In circuit control means, a source of electrical power,

first and second sets of light filaments producing different amounts of illumination, first and second transistors con nected between the source of electrical power and the first and second sets, respectively, of filaments to control the energization thereof, each transistor having a base, emitter and collector electrode, said collector electrodes of the first and second transistors being connected directly to the first and second sets, respectively, of filaments and each emitter electrode to the source of electrical power, first biasing means connected between the source of electrical power and one set of filaments and to the base electrode for the transistor connected to control the other set of filaments, second biasing means connected between the base of the other transistor and ground, and switching means connected between the base and emitter of the other transistor to cause alternate conduction of the transistors and alternate energization of the filaments upon switching action.

3. In circuit control means, a source of electrical power, first and second sets of light filaments producing different amounts of illumination, first and second transistors connected between the source of electrical power and the first and second sets, respectively, of filaments to control the energization thereof, each transistor having base, emitter and collector electrodes, the collector electrode of the first and second transistors being connected directly to the first and second sets, respectively, of filaments and each emitter electrode to the source of electrical power, a first biasing circuit connected between the source of electrical power and one set of filaments and to the base electrode for the transistor connected to control the other set of filaments, a second biasing circuit connected on one end to ground, on the other end to the source of electrical power, and to the base electrode of the other transistor, and switching means connected in the second biasing circuit to control alternately the biasing and conductivity of the first and second transistors and the alternate energization of the first and second sets of filaments.

4. Circuit control means as defined in claim 3 having resistance means in the collector circuit of one of the transistors to provide faster switching time from one condition to the other.

5. In circuit control means, automotive headlamps having upper and lower beam filaments, a source of electrical power, first transistor means having an input and an output circuit, said output circuit being connected between the source of electrical power and the upper beam filaments to control the energization thereof, switching means connected to the input circuit of the first transistor means to control the operation thereof, second transistor means having an input and an output circuit, said latter output circuit being connected between the source of electrical power and the low beam filaments to control the energization thereof, the input circuit of the second transistor means being connected to the source of electrical power and to the output circuit of the first transistor means, and biasing means connected to both first and second transistor means so that they are alternately conductive to switch from upper to lower beam energization and return upon operation of the switching means.

6. A circuit control means as defined in claim 5 having resistance means connected across the output of one of the transistor means to provide faster switching time.

References Cited UNITED STATES PATENTS 3,292,035 12/1966 Lee 315-83 JAMES W. LAWRENCE, Primary Examiner,

P. C. DEMEO, Assistant Examiner, 

1.IN CIRCUIT CONTROL MEANS, FIRST AND SECOND SETS OF LIGHT FILAMENTS PRODUCING DIFFERENT AMOUNTS OF ILLUMINATION, WHICH SETS IT IS DESIRED TO ENERGIZE ALTERNATELY, A SOURCE OF ELECTRICAL POWER, FIRST AND SECOND TRANSISTORS EACH HAVING A PAIR OF OUTPUT ELECTRODES AND A CONTROL ELECTRODE, THE OUTPUT ELECTRODES OF THE FIRST AND SECOND TRANSISTORS BEING CONNECTED BETWEEN THE SOURCE OF ELECTRICAL POWER AND THE FIRST AND SECOND SETS, RESPECTIVELY, TO CONTROL THE FLOW OF CURRENT THERETO, BIASING MEANS INTERCONNECTING THE SOURCE OF ELECTRICAL POWER AND THE CONTROL ELECTRODES 